Process and device for simulated moving bed separation with a reduced number of large diameter valves

Abstract

The invention concerns a simulated moving bed (SMB) separation device and process comprising a column, beds Ai of adsorbent separated by plates Pi with a single distribution and extraction network for fluids, in particular feed F, desorbant D, raffinate R and extract E, and a plurality of two-way valves for distribution of said fluids, said valves being limited in number and in particular with dimensions that are smaller than in the prior art. According to the invention, the column is divided into a plurality of sectors Sk with 2 superimposed plates, each sector Sk comprising an external principal bypass line Lk connected to each plate Pi of Sk via a large diameter plate valve Vi and an external secondary bypass line Mk comprising a small diameter valve VMk connected to the adjacent sector Sk−1. Each line Lk comprises a flow limitation means, and is connected to each of the fluid networks F, D, R, E via a single large diameter valve for sequential supply or withdrawal of the corresponding fluid F, D, R or E to or from the sector Sk under consideration.

Description

FIELD OF THE INVENTION[0001]The invention relates to the field of separation of natural or chemical products which are difficult to separate by distillation. A family of processes and associated devices is used which are known as “chromatographic” or “simulated moving bed” or “simulated counter-current” or “simulated co-current” separation devices which we shall hereinafter term “SMB”.[0002]A non-exclusive list of the fields concerned is:[0003]separation of normal paraffins from branched paraffins, naphthenes and aromatics;[0004]olefin / paraffin separation;[0005]separation of para-xylene from other isomers in C8 aromatics;[0006]separation of meta-xylene from other isomers in C8 aromatics;[0007]separation of ethylbenzene from other isomers in C8 aromatics.[0008]In addition to the refinery and petrochemicals plant, there are may other applications, including glucose / fructose separation, the separation of positional isomers of cresol, optical isomers, etc.PRIOR ART[0009]SMB chromatograp...

AI Technical Summary

Benefits of technology

[0030]The invention concerns an improved device for simulated moving bed separation belonging to the major SMB technique using a plurality of controlled two-way (on-off or progressive opening) valves, typically standard valves mass produced at the required high standard (seal / reliability) at low cost.

[0031]One of the essential aims of the invention is to reduce the relative disadvantage of this type of SMB, which is to require a large number of controlled large diameter two-way valves, i.e. with an opening diameter compatible with the movement of fluids in the SMB process at their nominal flow rate. Typically, the invention can substantially reduce the number of large opening diameter controlled valves while preserving the advantage of being able to use effective flushing of dead zones of the “long duration with a small or zero concentration gradient” type.

[0032]A further aim of the invention is to provide a device which requires a reduced number of two-way large (opening) diameter valves without the open / close frequency of those valves being increased with respect to the prior art; this along with the reduced number of large diameter valves limits the statistical risks of malfunction and thus increases the reliability of the system.

Problems solved by technology

A generic problem with all SMB devices is minimizing the pollution generated by the liquid present in the various zones and volumes of the supply and withdrawal circuits for the fluids and plates during modifications to the supply and withdrawal points during operation of the SMB.

Mixing or circulation over a short time interval of fluids with substantially different compositions thus introduces a deviation from the ideal operation, which proscribes discontinuities in composition.

A further problem may reside in any re-circulation between different zones of the same plate, which thus also induces a deviation from ideal operation.

However, since the flushing liquid typically has a composition which is very different from the liquid it displaces, this introduces discontinuities in the composition which are prejudicial to ideal operation.

The second technique uses only a single valve, but that single valve is a multi-way valve (more than 2 paths) and necessarily is of special construction, of large dimensions and extremely complex.

Further, this second technology excludes the possibility of asynchronous permutations, as in Varicol devices.

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